1. Field of the Invention
The present invention relates to a lens barrel and an imaging apparatus including openable/closable lens barriers which are provided in front of an imaging optical system in order to protect the imaging optical system.
2. Description of the Related Art
A conventional barrier device is, for example, discussed in Japanese Patent Laid-open No. 07-159856. The conventional barrier device includes a plurality of pieces of lens barriers which are rotatably supported by a lens barrel for holding a lens and a barrier drive ring which rotates around an optical axis to open and close the lens barriers. Further, the conventional barrier device includes barrier closing springs which are provided between the lens barriers and the barrier drive ring to allow the lens barriers to be constantly in contact with the barrier drive ring in order to bias the lens barriers in a closing direction of the lens barriers and which absorb an escaping movement of the barrier drive ring with respect to the lens barriers. Still further, the conventional barrier device includes barrier opening springs which are provided between the barrier drive ring and a lens barrel cover to bias the barrier drive ring in order to drive the lens barriers in an opening direction, and a connecting shaft which transmits a rotational force of a rotational barrel to the barrier drive ring.
Actions of the conventional barrier device having the above described configuration will be described below. A clockwise rotation of the rotational barrel serves to transmit a rotational force of the rotational barrel to a barrier drive ring through the connecting shaft. The barrier drive ring, upon receiving the rotational force, rotates in the clockwise direction with the barrier opening springs charged. The lens barriers rotate in a counter-clockwise direction following the barrier drive ring subject to the barrier closing springs as the barrier drive ring rotates in the clockwise direction. The lens barriers cover a front surface of the image optical system while the lens barriers rotate in the counter-clockwise direction. While the rotational barrel rotates in the counter-clockwise direction, a contacting portion between the rotational barrel and the connecting shaft is brought into a free movement.
The barrier drive ring rotates in the counter-clockwise direction due to a biasing force of the barrier opening springs having been charged. The lens barriers rotate in the clockwise direction as the barrier drive ring rotates in the counter-clockwise direction. The lens barriers cause the front surface of the imaging optical system to open owing to the rotation of the lens barriers. When the lens barriers are completely opened, the lens barriers are brought into contact with stoppers, which block their rotation in the clockwise direction. As a result, the barrier drive ring stops rotating.
For the sake of downsizing of the camera, shortening of an entire length of the lens barrel including the barrier device is effective. Therefore, an accommodation space for the lens barriers is effectively used when the barriers are in an opening state. For example, a barrier device as taught in Japanese Patent Laid-open No. 2008-033153 includes a space for accommodating the lens barriers while the lens barriers are open. When a lens barrel is in a retracted state, members of the lens barrel other than the lens barriers come into the accommodation space. At that time, the lens barriers are retreated from the accommodation space to be placed in a barrier closing state. Accordingly, the accommodation space for the lens barriers can be used effectively when the lens barrel is brought into the retracted state, and thus a thinner lens barrel can be obtained.
In the barrier device having the above described configuration, however, the lens barriers may interfere with the other members coming into the lens barrier accommodation space if the lens barriers cannot be closed only with the biasing force of the barrier closing springs because of, for example, a sticking foreign material on the lens barriers during the retracting movement of the lens barrel. In view of the above, in Japanese Patent Laid-open No. 2008-033153, contact units for closing the lens barriers, are provided on the barrier drive ring which presses the lens barriers in the opening direction during an opening movement of the lens barriers. The contact units press the lens barriers in the closing direction to forcibly drive the lens barriers in the closing direction if the foreign material or the like is stuck on the lens barriers and the barriers cannot be closed only with the biasing force of the barrier closing springs. Accordingly, the lens barriers are prevented from interfering with the other members of the lens barrel.
However, the barrier device of Japanese Patent Laid-open No. 2008-033153 has such a configuration that a relative movement between the lens barriers and a barrier drive member forcibly drives the lens barriers in the closing direction. The above described configuration is not applicable to a barrier device in which the lens barrier is supported by the barrier drive member in a rotational manner and the lens barriers moves in synchronization with the barrier drive member when the barrier drive member rotates from its position at the time of opening the lens barriers to its position at the time of closing the lens barriers. This is because, in the above described barrier device, the lens barriers could not be closed forcibly by the barrier drive ring since the barrier drive ring did not move relative to the lens barriers.